1. Field of the Invention
The invention is directed to shorting switches and, in particular, to shorting switches for eliminating arcing faults in low voltage power distribution equipment. The invention is also directed to shorting systems for eliminating arcing faults in low voltage power distribution equipment.
2. Background Information
There is the potential for an arcing fault to occur across the power bus of a motor control center (MCC), another low voltage (LV) enclosure (e.g., an LV circuit breaker panel) and other industrial enclosures containing LV power distribution components. This is especially true when maintenance is performed on or about live power circuits. Frequently, a worker inadvertently shorts out the power bus, thereby creating an arcing fault inside the enclosure. The resulting arc blast creates an extreme hazard and could cause injury or even death. This problem is exacerbated by the fact that the enclosure doors are typically open for maintenance.
It is known to employ a high-speed shorting switch, placed between the power bus and ground, or from phase-to-phase, in order to limit or prevent equipment damage and personnel injury due to arc blasts. It is also known to employ various types of crowbar switches for this purpose. The switches short the line voltage on the power bus, eliminating the arc and preventing damage. The resulting short on the power bus causes an upstream circuit breaker to clear the fault.
Examples of medium voltage devices include a stored energy mechanism with vacuum interrupter contacts, and a mechanism to crush a conductor magnetically.
An example of a low voltage device is a stored energy air bag actuator, which drives a conductive member having a pin and a flange, in order to short two contacts. The first contact is in the form of a receptor for capturing the pin of the driven conductive member. The second contact has an opening, which allows the pin to pass therethrough, but which captures the flange of the driven member.
There is room for improvement in shorting switches and systems that respond to arcing faults and switch fast enough in order to protect workers and equipment from arc blasts associated with LV power distribution equipment.
These needs and others are met by the present invention, which provides a shorting switch for low voltage applications, which switches fast enough to protect personnel and equipment, while maintaining suitable electrical contact in order to eliminate subsequent arcing. The shorting switch employs a simple and low cost spring energy storage and fractured release member mechanism. The fractured release member actuates a spring-loaded contact, which then electrically engages two or more contacts. The spring has a suitably high force in order to maintain suitable contact force to prevent contact blow-apart and subsequent arcing.
As one aspect of the invention, a shorting switch for eliminating arcing faults in low voltage power distribution equipment comprises: a base supporting a first side and an opposite second side; a spring having a first end engaging the first side of the base, the spring also having a second end; a release member having an opening therein, the release member having a first end engaging the first side of the base, the release member also having a second end; a charge disposed in the opening of the release member, the charge for fracturing the release member; a bridging contact biased by the second end of the spring toward the second side of the base, the second end of the release member normally maintaining the spring in a compressed state; two contacts supported by the second side of the base for electrical engagement by the bridging contact after fracture of the release member; and two terminals respectively electrically connected to the two contacts.
As another aspect of the invention, a shorting switch for eliminating arcing faults in low voltage power distribution equipment comprises: a base supporting a first side and an opposite second side; a spring having a first end engaging the first side of the base, the spring also having a second end; a release member having an opening therein, the release member having a first end engaging the first side of the base, the release member also having a second end; a charge disposed in the opening of the release member, the charge for fracturing the release member; a bridging contact biased by the second end of the spring toward the second side of the base, the second end of the release member engaging the bridging contact to normally maintain the spring in a compressed state; at least three contacts supported by the second side of the base for electrical engagement by the bridging contact after fracture of the release member; and at least three terminals respectively electrically connected to the at least three contacts.
As another aspect of the invention, a shorting system for eliminating an arcing fault in low voltage power distribution equipment comprises: a base supporting a first side and an opposite second side; a spring having a first end engaging the first side of the base, the spring also having a second end; a release member having an opening therein, the release member having a first end engaging the first side of the base, the release member also having a second end; a charge disposed in the opening of the release member, the charge for fracturing the release member; a bridging contact biased by the second end of the spring toward the second side of the base, the second end of the release member normally maintaining the spring in a compressed state; two contacts supported by the second side of the base for electrical engagement by the bridging contact after fracture of the release member; two terminals respectively electrically connected to the two contacts; and means for detecting an arcing fault and responsively activating the charge disposed in the opening of the release member, in order that the activated charge fractures the release member, which releases the spring, which drives the bridging contact to short across the two contacts to eliminate the arcing fault.